This required migrating to pyproject-flake8 as flake8 proper still doesn't support pyproject.toml.

Wheel cannot use pep517 yet because the installation process involves installing wheel because the setuptools build backend declares it as a dependency for building wheels. A future update of pip may solve this problem.

Setuptools_scm, on the other hand, requires wheel as a build time dependency so if somebody tries to install wheel using `--no-binary=:all:`, it also creates a circular dependency.

Fixes #332.

New versions are now made by declaring a new version in the changelog (docs/news.rst) and pushing this change to Github. The workflow will see this version and create a new tag which then triggers the release workflow.